Railway traffic controlling apparatus



Dec. 14, 1943.

L R. ALL| soN ETAL RAILWAY TRAFFIC CONTROLLING APPARATUS 2 Sheets-Sheet 1 Filed March 16, 1943 INVEN TOR$ LerlzeHAZlwon mad BY @Pl Va z.

771513 ATTORNEY Dec. 14, 1943. R. ALLISON ETAL 2,336,766

RAILWAY TRAFFIC CONTROLLING APPARATUS Filed March 16, 1943 I 2 Sheets-Sheet 2 0 AmpQl -f Gonepafop Vblffi 2 426293032 3436594 and I and Volzfrz I 5 Valli/1 THEIR ATTQ R N EY i atented Dec. 14, 1943 iJNl'lEfi STATES estates @ATENT OFFECE.

RAILNAY TRAFFEC CONTROLLING APPARATUS Application March 16, 1943, Serial No. 479,354

13 Claims.

Our invention relates to railway traflic controlling apparatus, and more particularly to train carried train control apparatus responsiv to coded energy.

Ihe present application is a continuation-inpart of our copending application Serial No. 455 178, filed August 18, 1942, for Railway traffic controlling apparatus.

Apparatus of this type normally uses a trackway circuit including the track rails, and to which circuit an alternating current coded by being periodically interrupted at any one of several difierent code rates is supplied, a different code rate being assigned to each of several different traffic conditions. Energy is transferred from such track circuit to a train carried receiver mounted on a train in inductive relation to the rails, an electromotive force of the frequency and code of the rail current being thus induced in the receiver. The received electromotive force is used to operate a train carried code following relay which in turn governs train controlling devices through a decoding means that is selectively responsive to the code rate at which the relay is operated. The received electromotive force is of a relatively low energy level and an amplifier is interposed between the receiver and the code following relay. The requirements of such an amplifier are exacting and much inventive thought has been directed thereto and many different forms of amplifiers have been proposed and tried out.

The requirements of such an amplifier are exacting because safety of operation must be as nearly 100 per cent as can be reasonably obtained. Its sensitivity must be set to assure satisfactory broken rail and shunting protection. A substantially uniform energy level of amplifier output must be maintained over a relatively wide range in the amplitude of the received electromotive force as caused by variations in the amplitude of the rail current due to different local conditions of the difierent track sections and due to the shunting out of the rail impedanc as a train moves from the entrance end to the exit end of the track circuit. The amplifier must be immune to extraneous energy picked up by the receiver due to the rails carrying propulsion current and stray currents from power systems. The local train carried current source from which energy is derived for en ergizing the amplifier may vary widely in its voltage. Code distortion must be minimized. False operation due to a broken or misplaced circuit element must be avoided. Ample tolerance must be allowed for manufacturing variations in the electron tube employed in the amplifier. Severe vibrations and shocks due to train movements occur. Interchangeability with present amplifiers is desirable, and simplicity of construction, low cost and little maintenance are essential.

Accordingly, a feature of our invention is the provision of railway traffic controlling apparatus incorporating novel and improved means for amplifying coded alternating current.

Another feature of our invention is the provision of train control apparatus incorporating a novel low voltage electron tube amplifier Wherewith energy from the usual 32 volt train lighting current source is used without voltage conversion.

Still another feature of our invention is the provision of train control apparatus incorporating a novel low voltage electron tube amplifier operable from the usual 32 volt direct current train source and wherewith a substantially constant predetermined energization of a code following relay is maintained irrespective of voltage variations of such train source and of variations in the effective value of th associated alternating track circuit current.

Again, a feature of our invention is the provision of a low voltage electron tube amplifier that is interchangeable with the multiple stage high voltage tube amplifier commonly used in train carried train control apparatus.

Another feature of our invention is the provision of train control apparatus incorporating an electron tube amplifier constructed to substantially eliminate false operation due to open circuit conditions.

Other features, objects and advantages of our invention will appear as the specification progresses.

To obtain the above features, objects and advantages embodying our invention, we provide a receiver, a filter, special low voltage high vacuum electron tubes, fixed and automatic grid bias voltage means, a master transformer, and a code following relay, and which elements are so correlated with respect to each other as to form an amplifier unit that will in its operation meet the exacting requirements of the particular service here involved.

We shall describe two forms of apparatus embodying our invention, and shall then point out the novel features thereof in claims.

In the accompanying drawings, Fig. 1 is a diagrammatic view showing train carried train con trol apparatus using one form of a single stage amplifier unit embodying our invention. Fig. 2 is a diagrammatic view showing train carried train control apparatus using one form of a two stage amplifier unit embodying our invention. Figs. 3, 4 and are diagrams showing operating characteristics of the apparatus of Figs. 1 and 2.

In the different views like reference characters are used to designate similar parts.

Referring to Fig. 1, the reference characters la and lb designate the track rails of a railway, which rails are formed in the usual manner with a track section provided with a track circuit including the rails and a current source connected across the rails at the exit end of the section, and which current is coded at any one of a plurality of different code rates according to different trafiic conditions. The trackway apparatus for supplying such coded current to rails la and lb is not shown since it forms no part of our present invention. It may be of any one of several wellknown arrangements, such as, for example, that disclosed in Letters Patent of the United States No, 1,986,679, granted January 1, 1935 to L. V. Lewis, for Railway traflic controlling apparatus. In order to better understand our invention, the alternating current supplied to rails la and lb will be considered as having a frequency of 100 cycles per second and as being coded at 180, 120 and '75 interruptions per minute to reflect clear, approach-medium and approach traffic conditions, respectively, and the absence of rail current or the presence of non-coded rail current reflects a slow speed traffic condition. It will be understood, however, that our invention is not limited to the above-mentioned frequency and code rates.

The train carried apparatus comprises a receiver, an amplifier unit, a decoding unit and a train controlling device or signaling means.

The receiver includes two inductors 2 and 3 mounted on the train in inductive relation to rails la and lb, respectively, for an alternating electromotive force to be induced in each inductor 2 and 3 when alternating current fiows in the rails. The windings of the two inductors are preferably connected to add the electromotive forces induced therein when current flows in opposite directions in the track rails at any given instant. It follows that with coded alternating current supplied to the track circuit including the rails la and lb, an alternating electromotive force is received on the train through inductors 2 and 3, the electromotive force having a frequency and code rate corresponding to those of the rail current. Also, for a given unit or pick-up value of rail current the received electromotive force will have a given amplitude and will vary in amplitude in accordance with variations in the amplitude of the rail current. Inductors 2 and 3 are connected by wires 4 and 5 to the input terminals TC and FT of an amplifier unit AM.

This amplifier unit AM comprises a filter Fl, an electron tube ET, a master transformer MT, a code following relay CF, a biasing unit BU, biasing resistors Rl and R2, condensers Cl and C2 and the necessary circuit connections.

Filter Fl consists of condensers l5 and l and a transformer Tl having independent primary and secondary windings 8 and 9, respectively. The primary winding 3 of transformer Tl is connected in series with condenser 6 across the input terminals TC and FT, and condenser 'l is connected across the secondary winding 9 of the transformer. Filter Fl is tuned to resonance at the frequency of the track circuit current, which in the case here assumed is cycles per second. Hence the coded alternating electromotive force received by inductors 2 and 3 due to the track circuit current is passed by filter Fl with little attenuation, but electromotive forces picked up by the inductors due to extraneous currents of other frequencies are substantially suppressed. With the tuning and coupling of the filter once established, the voltage appearing across secondary winding 9 and condenser l in multiple is predetermined for a given value of rail current. The electromotive force passed by filter Fl is applied to the control grid of electron tube ET and in order to select or adjust the voltage of the electromotive force to be applied to the electron tube and maintain the tuning and coupling factor of the filter undisturbed, we provide secondary winding 8 of transformer Tl with intermediate terminal taps to any one of which the grid circuit for the electron tube to be shortly described can be connected.

Electron tube ET may be any one of several different types and is preferably a high Vacuum indirectly heated cathode tube. As disclosed tube ET has a filament or heater l d, an anode or plate I l, a cathode if, a control grid l3 and a screen grid l6. Tube ET is designed for operation from a single 32 volt source of direct current, it being contemplated that the usual train lighting generator Will serve as the source of energy for the amplifier unit. When the apparatus is mounted on a steam locomotive energy may be taken from the steam turbo headlight generator. We do not limit our invention, however, to such source of energy and a special generator or battery may be used. In Fig. 1, the source of energy is indicated as a generator G which is cap-able of supplying a 32 volt direct current and whose positive and negative terminals are connected to power terminals B32 and N32, respectively, of the amplifier unit. It should be pointed out that the usual train carried headlight generator may vary greatly in its output voltage. In other words, the voltage of generator G may vary over a relatively wide range and the amplifier unit AM is arranged for proper operation at all voltages within a range of say, 26 to 40 volts.

The tube ET is provided with a heater or filament circuit and a plate circuit which are independently connected in multiple to the 32 volt current source and with a control grid circuit which is coupled to the receiver through the filter. The heater or filament l l is connected across terminals B32 and N32 through a resistor l5 and the tube ET is constantly heated by this filament circuit. It should be pointed out that biasing resistors R! and R2 are connected in series across the power terminals B32 and N32 and are provided with a. junction or mid terminal it to which cathode l2 of the tube is connected by wire 22 so that resistor R2 is common to both the plate and grid circuits. The plate circuit can be traced from terminal B32 through lead wire 27, primary winding 23 of transformer MT in multiple with condenser C2, lead wire 24, plate l l and tube space to cathode l2, wire 22, junction terminal l6 and resistor R2 to terminal N32. The control grid circuit can be traced from grid l3 through wire l8, secondary winding 9 of transformer Tl to a preselected intermediate terminal l9, biasing unit BU, resistor R2, mid terminal l6 and wire 22 to cathode l2.

It is clear that control grid l3 is provided with a fixed negative grid bias voltage equal to the voltage drop across resistor R2 due to biasing resistors R! and R2 being connected across the 32 volt direct current source. Resistor R2 is preselected to provide a fixed negative grid bias voltage that establishes a predetermined normal plate circuit current is maintained constant over plate circuit current and which value of normal a relatively wide range of variations in the output voltage of the direct current source, because the voltage drop across resistor R2 varies directly with variations of the voltage of the supply source.

It should be pointed out that the filament iii of tube ET does not vary in resistance directly with variations in the current caused by changes in the supply voltage but has stabilizing characteristics similar to that of a ballast lamp. We have found that the filament resistor, such as resistor l which has heretofore been used as a source of a fixed grid bias voltage, does not give a voltage drop which varies directly with the variations of the voltage of the supply source due to the ballast lamp effect of the tube filament, and that derivin a bias voltage from a Voltage divider, such as resistors R! and R2, independently connected across the current supply source is a much superior method when the plate and filament circuits are energized from a common source. This is so since, for a given voltage applied to the plate and filament, the plate current of the tube is proportional to the grid bias voltage, and it is essential to have the fixed grid bias voltage vary directly with the voltage of the current source so as to obtain more nearly perfect compensation for the variations of the voltage applied to the plate and filament which tend to change the value of the plate current. This is especially true for a low voltage electron tube because the plate current varies greatly for changes in plate and filament voltage and the fixed grid bias voltage is of a critical value. Since resistors Bi and R2 of the voltage divider or fixed grid bias voltage means are proportioned for predetermined resistances, the voltage of junction terminal 56 varies directly with the voltage of generator G and the normal plate current is maintained substantially uniform. Also, such a voltage divider has the advantage over a filament circuit resistor because diiierent tubes have filaments or" diilerent resistance. Furthermore, resistors R1 and R2 are proportioned so that the desired bias voltage is obtained from terminal i i with resistor R2 of a relatively low resistance. This is also desirable so that the alternating voltage drop created across this resistance due to the alternating current component of the plate circuit current during the on code period of the coded rail current creates little reverse feed back action.

It is apparent that the coded alternating electromotive force picked up by inductors 2 and 3 due to the track circuit current is passed by filter F! and applied to the grid circuit of tube ET, and the portion of this electroinotive force to be applied to the grid circuit can readily be preselected by changing the intermediate terminal connection of secondary winding 9 and such preselection can b made Without in any way disturbing the tuning and coupling factor of the filter. We have found that such a construction has decided advantages because the parts can be set up at the factory for proper tuning and coupling factor and a final connection readily made in the field after the apparatus is installed on the locomotive so as to obtain satisfactory broken rail and shunting protection for the track circuits of the particular railroad over which the locomotive operates. Also, when the locomotive is to be operated over any one of two or more divisions having track circuits of different lengths and different normal eiiective values of rail current, the train control apparatus can be quickly and reliably adjusted at the engine house to suit the particular division.

The tube ET is automatically biased by a voltage derived from biasing unit BU, which consists of a resistor 2 and a condenser 2! connected in multiple, a voltage being built up on biasing unit BU in a manner to be explained when the operation of the apparatus is described.

Master transformer MT and its associated bypass condenser 02 are provided With a special construction. Primary winding 23 of transformer MT is constructed with four lead wires 2%, 2'5, 26 and 21, two for each end of the winding. The two lead wires for each end are connected toget-her within the Winding. Leads and 28 are connected to condenser C2 and the leads 24 and iii! are connected to plate H and positive terininal 1332, respectively. Condenser C2 serves to by-pass the alternating component of the plate circuit current but the code variation, that is, the increase and decrease caused in the average value of the plate circuit current, due to the on and off code periods of the received electromotive force induce electromotive forces in secondary winding 28 of transformer MT in the well-known manner to energize code following relay CF Whose operating winding 29 is connected across secondary winding 28. Code following relay CF is preferably a stick polar relay operable in response to a predetermined value of energize.- tion. Such special construction of the master transformer has the utility in that it materially aids in avoidin false operation of relay CF due to an intermittent open circuit condition, as will be pointed out more fully during the description of the operation of the a paratus.

An impedance, such as a condenser Cl, is con nected across control grid 53' and cathode 52 to act as a reservoir and maintain the negative grid bias voltage when the grid circuit is opened for any reason. Grid M is connected to the positive terminal B32 and serves as a screen grid to improve the operation of the tube, the parts being so proportioned that the tube becomes inoperative if the screen grid it becomes disconnected.

The decoder unit is indicated as a Whole by the dash rectangle DU and comprises a decoding transformer DT, three decoding circuits DCI, D02 and D03, and three decoding relays A, R and L. The two portions of primary winding 3% of transformer D1 are supplied with direct current from generator G through polar contacts 3i and $2 of code following relay CF, so that an alternating electromotive force is induced in secondary winding 33 of transformer DT when relay CF is operated, the frequency of such electremotive force corresponding to the rate at which relay CF is operated. Secondary winding of transformer DT is connected to the decoding circuits in multiple. Decoding circuit DO! consists of condenser 34 and an inductance at least a portion of inductance 35 being connected to the decoding relay A through a full wave rectifier 815. This circuit DC! is tuned to resonance at the frequency of the electroforce induced in secondary winding 33 in e to operation of relay CF at the rate corresponding to the 189 code rate, and consequentlyf 4 aseavee relay A is energized and picked up in response to rail current of the 13% code rat Circuit DCZ consists of a condenser 37 and an inductance at least a portion of inductance 38 being connected to the decoding relay R through a full wave rectifier 33. This circuit D62 is tuned to resonance at the frequency of the electromotive force induced in secondary winding in response to operation of relay CF at the rate corresponding; to the 120 code rate and consequently relay R is energized and picked up in response to rail current of the 12s code rate. Circuit DC-S includes an inductance it, at least a portion of which is connected to decoding relay L through a full wave rectifier i i. This circuit DC3 is nontuned and hence relay L is energized and picked up when relay CF is operated at a rate corresponding to one of the 160, 120 or 75 code rates.

As here shown, the train controllin device CS is a position light cab signal capable of displaying four different signal indications and supplied with. current from generator G. This signal is controlled by the decoding relays A, R and L, the arrangement being such that when relay A is picked up to close front contact a circuit is closed for lamp of signal CS and that lamp is illluminated to display a clear signal indication; when relay A is released closing back contact G4 and relay R is picked up closing front contact a circuit is closed for lamps 2 a and s? in multiple so that these lamps are illuminated to display an approach-medium signal indication; when relays A and R are released closing back c tacts A l and 48, respectively, and relay L is picked up closing front contact 39, a circuit is closed for 5t and that lamp is then illuminated to display an approach signal indication;

when relays A, R and L are all released closing back contacts M, 3,8 and El, respectively, a circuit is closed for lamp 5?; and that lamp is illuminated to display a slow speed signal indication.

In describing the operation of the apparatus, we shall first consider that generator G supplies current at its intended voltage of 32 volts, and no rail current is flowing to induce an electromotive force in the receiver. Under this condition, the bias voltage derived from resistor R2 for electron tube effects a normal value of plate current, the parts being preferably proportioned so that the normal plate current is of the order of 0.5 milliampere. If the voltage supplied by generator G changes, the bias voltage derived from resister R2 will correspondingly vary so that the plate circuit current will remain at substantially the some normal value for all voltages of generator between the limits of say 26 volts and 40 volts. We have found that with an amplifier operating from the 32 volt current source it is essential that the normal value of the plate circuit current be confined within very narrow limits to assure proper operation of the apparatus. We have also found that with the normal plate current mentioned above and the primary winding 23 or master transformer MT constructed in the described hereinbefore with four separate leads, the energy transferred through seccndarv winding 28 to relay CF due to an intermittent open circuit condition at any one of the plate circuit elements is insuflicient to operate relay CF. Furthermore, with the construction here disclosed, to obtain a false operation of relay CF by an intermittent open circuit of a plate circuit element, the normal or residual plate current must excee 3 milliamperes. Also a false operation of relay CF under the normal conditions here assumed can occur only if the intermittent open circuit occurs in the primary winding 23 itself, but an intermittent open circuit at a code rate within the winding of the transformer is extremely improbable.

Condenser C l which is connected between control grid l3 and cathode I2, is charged at a potential substantially equal to the normal negative grid bias voltage. If condenser Cl is not used an open circuit condition occurring in the grid circuit might permit a rapid leaking off of the negative bias voltage of the control grid with the result that a rapid variation would occur in the plate circuit current which in turn might transfer suiiicient energy through transformer MT to operate relay CF. However, condenser Ci acts as a reservoir and maintains the negative grid bias voltage for a period if the grid circuit is opened, and a very gradual leaking off of the grid bias voltage occurs so that the variation of the plate circuit current is so gradual that substantially no energy is transferred through transformer MT to relay CF. It is clear, therefore, that we have provided a construction for the amplifier unit by which the normal plate circuit current is maintained at a substant ally uniform value and by which false operation or" the code following relay due to an intermittent open cir cult condition is practically eliminated.

We shall now assume that alternating current coded at the code rate is supplied to ra ls in and lb, the amplitude of the rail current being of a preselected pick-up value such as, for example, 1.4 amperes. The electromotive force received by inductors 2 and 3 is of a corresponding value and the desired input electromotive force for electron tube ET can be selected by con necting the grid circuit to the proper one of the taps, such as intermed ate tap iii of the secondary win-ding 9 of transformer Tl such selection being made with the tuning and the coupling of the filter maintained unefiected Each positive half cycle of this received electromotive force drives control grid E3 in the positive direction in opposition to the fixed negative bias voltage derived from resistor R2, and plate current flows. Hence there is an increase in the value of the plate cur rent during each on code period of the coded current and the plate current decreases to substantially its normal value during each on code period. Such code variations of the value of the plate circuit current induce electromotive forces of opposite polarity in secondary winding 23 with the result that code following relay CF is alternately energized with currents of opposite polarities and is operated at a rate corresponding to the 180 code rate of the rail current. The parts are so proportioned and the connection to filter Fl so selected that the pick-up value of the rail current creates a predetermined energization of relay CF and which energization of relay CF is just equal to that required for proper operation of the relay, the relay being neither over-energized nor under-energized. Hence the relay is operated in step with the on and oil code periods without code distortion created in the energy supplied through the contacts of relay CF to the decoder unit. With relay CF operated at a rate corresponding to the 180 code rate, decoding relay A is energized and picked up to cause signal CS to display its clear signal indication.

In Fig. 4 the plate current of tube ET is shown as a function of the received eleotromotive force when the preselected pick-up value of rail current fiows. Looking at Fig. 4, the line GB indicates the normal negative grid bias voltage derived from resistor R2, the plate circuit current being or a value of the order of 0.5 milliampere. The alternating electromotive force applied to control grid 13 of the tube ET is represented by the graph just below the horizontal axis, that is, the alternating electromotive force for one code cycle of rail current of the pick-up value is illustrated. The resultant plate current for this one cycle of received electromotive force is represented by the graph to the right of the vertical axis, the plate current increasing to a predetermined average value during the on code period and decreasing substantially to its normal value during the off code period.

In the event the voltage of generator G increases above the designated value of 32 volts, the voltage drop through resistor R2 increases and the negative grid bias voltage is increased to compensate the increase that would be caused in the plate circuit current due to such increase in the supply Voltage. Conversely, if the generator voltage falls below the designated value of 32 volts,

the bias Voltage derived from resistor R2 is corcurrent of about 1.4 amperes, the compensation of the amplifier effected through the bias resistor R2 maintains the energization of relay CF substantially uniform at its desired working value throughout-the range of 26 to 40 volts of the generator G.

We shall next assume that at the exit end of a track circuit the amplitude of the rail current increases above the pick-up value and the received electromotive force is correspondingly increased. With an increased value of received electromotive force the higher values of each positive half cycle would drive control grid l3 positive in potential with respect to the cathode l2, causing grid current to how, and with grid current flowing conr denser 2! of biasing unit BU is charged to a voltage substantially equal to the difierence between the peak voltage of the received electromotive force and the normal negative grid bias voltage. The time constant of the biasing unit BU is predetermined and is made such that th voltage developed across condenser 2! during an on code period is retained with little loss during the next on code period or at least until the output voltage of filter Ft reaches zero after the rail current is interrupted with the result the biasing voltage attained through resistor R2 is increased by the automatic bias voltage developed in unit EU. The resultant bias voltage for tube ET tends to maintain a nearly uniform code variation in the plate current for a relatively wide variation in the rail current amplitude. This characteristic of the apparatus is illustrated in Fig. 5, from an inspection of which we believe this characteristic will be apparent without further explanation.

Th operation of the apparatus when current of either the 120 or 75 code rate is applied to the rails will be readily understood from an inspection of the drawings taken in connection with the foregoing description of the operation of the apparatus in response to rail current of the 180 code rate.

Referring to Fig. 2, the train carried apparatus is the same as in Fig. 2, except the single stage amplifier unit AM is replaced by a two stage amplifier unit AMI for use with track circuit currents of a relatively low amplitude and the description of the apparatus of Fig. 2 will be confined to that of the amplifier unit.

The amplifier unit AMI comprises a filter Fl, a first stage tube ETI, a second stage tube E'IZ, a coupling transformer T2, master transformer MT and its associated condenser 02, code following relay CF and fixed and automatic bias means for each of the two tubes. The filter Fl, master transformer MT, and relay CF are the same as in Fig. 1, and the description of these devices need not be repeated. Tubes ET! and ET2 are preferably alike and each is preferably of the same indirectly heated type as tube ET of Fig. 1.

Referring to first stage tube ETi, its filament 55 is connected across power terminals B32 and N32 through resistor 55, and its plate circuit includes terminal B32, winding 5'! of coupling transformer T2, plate 58 and intervening tube space to cathode 5d, resistors till and 56 and terminal N32. The control grid circuit for tube ET! extends from grid 6! through condenser 62, secondary winding ii of transformer Ti to preselected intermediate terminal lfi, and resistors 56 and 65 to cathode 59. A resistor 63 is connected between grid BI and the negative terminal of the power source. It is to be seen that resistors 56 and Gil form a bias means from which a grid bias voltage for tube ET! is derived, such bias voltage being equal to the voltage drop across resistor 56 due to the filament current plus the voltage drops across resistors 69 and 56 due to the plate current. Resistor 66 is made large as compared to resistor 58 so that each resistor has about the same voltage drop and the two resistors are preselected to provide a resultant grid biasvoltage that efiects a predetermined normal value of plate current. For example, the resistors are preselected to provide a bias voltage that preferably gives a normal plate current of the order of 1.0 milliampere, resistor 60 being many ohms larger than resistor 55. With such construction the grid bias voltage varies so nearly in direct proportion to the voltage of the power source that the plate current is maintained substantially uniform. This is so because resistor 66 is large and the portion of the bias voltage provided by the plate current flowing therethrough is about equal to that provided by the filament current flowing in resistor 56 and the ballast lamp characteristic of filament 55 due to the filament current is of little effect on the resultant biasvoltage. Thus when the filament and plate circuits are connected in multiple to the same source of power a resistor in the plate circuit and a resistor common to both the plate and filament circuits can be proportioned to form a bias means that provides a bias voltage that varies substantially directly with the voltage of the power source to maintain a substantially uniform value of plate current over a relatively wide range of voltages of the power source.

The condenser 62 and resistor 63 of the grid circuit form an automatic bias means that functions in substantially the same way as the bias unit BU of Fig. l.

Resistor 53 being connected directly to grid 6! and the negative terminal, it also functions as a connection to maintain the fixed grid bias voltage in case an open circuit occurs in the grid circuit. Consequently, such an open circuit condition is not followed by a rapid rise of plate current which might otherwise be repeated through the amplifier to cause an operation of the code following relay. An open circuit at resistor 56 or 58 would be followed by zero plate current and since the normal plate current is made small such a variation of plate current is not SLlffiCieIlt to cause an operation of the relay.

Referring to second stage tube ETZ, its filament and plate circuits are independently connected to the power source, its control grid cir-- cult is coupled to the plate circuit of the first stage tube and fixed and automatic grid bias means are associated therewith. The filament 54 of tube ET2 is connected across terminals B32 and N32 through resistor 65. Resistors RI and R2 are connected in series across the power terminals and provided with a junction terminal it the same as in Fig. 1, and resistor R2 is common to both the plate and grid circuits to form a bias means for tube E'I2. The plate circuit includes primary winding 23 of transformer MT, plate 66 and intervening tube space to cathode 57 and resistor R2; and the control grid circuit includes grid 68, condenser 69, winding 70 of coupling transformer T2, resistor R2 and cathode 6?. A condenser H is connected across transformer winding 78 and a resistor 12 is connected between grid 68 and the negative terminal of the power source.

Thus tube ETZ is provided with a fixed grid bias voltage from resistor R2 and which voltage varies directly with the voltage variations of the power source so that a substantially uniform normal plate current is maintained for this secnd stage tube. Preferably this fixed bias voltage is such as to cause the normal plate current to be substantially zero or of the order of (5.5 milliampere.

Condenser H serves to tune the coupling transformer T2 to resonance at the frequency of the alternating current. Condenser 69 and resistor 72 form an automatic grid bias means similar to unit BU of Fig. 1. Resistor 12 also functions as a connection to maintain the fixed grid bias for tube ET2 in case of an open circuit condition of its grid circuit and a rapid rise of plate current of tube ETZ due to loss of grid bias voltage because of such open circuit condition is avoided. Such change in plate current might otherwise be sufficient to cause an operation of relay CF.

The master transformer MT of Fig. 2 is constructed with four separate leads 24, 25, 2S and 27 from its winding 23 for connection to condenser C2 and the plate circuit of tube ET2 the same as in Fig. 1 to avoid false operation of relay CF due to an intermittent open circuit condition.

Grids i3 and 74 of tubes ETI and ET2, respectively, are each connected to the positive terminal of the power source and each functions as a screen grid to improve the operation of the respective tube, each tube becoming inoperative if its screen grid connection becomes open circuited.

It is to be seen from the foregoing description that each tube of the amplifier unit AMI is provided with a normal bias voltage that establishes a predetermined normal value of plate circuit current for the respective tube and such bias voltage substantially varies directly with the voltage of the power source to maintain the plate current substantially uniform. Also the circuits are constructed so that an open circuit condition does not give rise to a rapid change in a plate current of a magnitude that may cause false operation of the code following relay.

When an electromotive force is received in response to coded track circuit current, such electromotive force is applied to the grid circuit of the first stage tube ET! to be amplified and repeated at transformer T2 and applied to the grid circuit of the second stage tube for further amplification. The value of the received electromotive force to be thus applied is preselected by selection of the intermediate terminal of winding 8 at the filter transformer. Code detection is eifected at master transformer MT and its associated condenser C2 and relay CF is operated at a corresponding code rate for governing the decoding unit DU and in turn the cab signal CS. In the event the amplitude of the tracl: circuit current becomes large the automatic bias means of the tubes function to reduce the amplification gain so that the energization of relay CF is substantially the same for a large tract: circuit current as it is lor current of normal amplitude and code distortion at the relay is avoided. Also when the rail current is large and the filter overexcited so that oscillations of large amplitude persist in the filter during an off code period, the automatic bias means functions to suppress the higher values of such oscillation and minimize any code distortion that might result from such oscillations.

We have found that the single stage amplifier unit disclosed in Fig. 1 is interchangeable with the present day multiple stage high voltage amplifier unit used in train carried train control apparatus, sufiicient energy being made available by this single stage amplifier for reliable operation of a standard code following relay and decoding means when rail currents of the usual amplitude are used. The two stage amplifier unit disclosed in Fig. 2 is not only interchangeable with the present multiple stage high voltage amplifier but is effective to operate a standard code following relay when rail currents of relatively low amplitude are used to increase broken rail protection and shunting sensitivity, as well as to reduce the required track circuit energy. Furthermore. low voltage amplifier units, the elements of which are constructed and correlated in the manner we have disclosed, are characterized by a high degree of safety and uniformity of operation, and are of low cost.

Furthermore, such an amplifier can be constructed at the factory for proper tuning and coupling factors and then readily adjusted in the field to the track circuits with which it is to be used with the tuning and coupling unaffected.

Although we have herein shown and described but two forms of railway traffic controlling apparatus embodying our invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim is:

1. In train control apparatus using a receiver mounted on a train for inductively receiving an electromotive force in response to a coded alternating track circuit current and a code following relay coupled to the receiver through an amplifier unit for operating the relay in response to such electromotive force; an amplifier unit including in combination an electron tube, a filter and a grid bias means; said tube operable from a 32 volt source of direct current and having a filament and a plate circuit independently connected to said direct current source to create a predetermined plate circuit current when a given grid bias voltage is used, said tube having a control grid circuit coupled to said receiver by a circuit means to create code variations in the plate circuit current in response to said electromotive force, said filter comprising a first and a second condenser and a transformer having separate primary and secondary windings with the secondary winding constructed to have multiple intermediate taps, said filter disposed with said primary winding and first condenser connected in series to said receiver and said second condenser connected across the full portion of the secondary Winding, and said filter tuned to resonance at the frequency of said alternating current to suppress energy other than said electromotive force and connected to said circuit means at a preselected one of said intermediate taps to preselect with the tuning maintained undisturbed the value of the electromotive force applied to said grid circuit to predetermine the code variation created in the plate current, said grid bias means comprising a first and a second resistor connected across said direct current source and having a junction terminal to which said grid circuit is connected to provide said given bias voltage and to vary such bias voltage directly with the voltage of said direct current source to compensate for variations in the voltage applied to the plate circuit, and said plate circuit coupled to said relay for operation of the relay in response to the code variations thus created in the plate current.

2. In train control apparatus using a receiver mounted on a train for inductively receiving an electromotive force in response to a coded alterhating track circuit current and a code following relay operable to govern signaling means when provided with a predetermined energization and coupled to said receiver through an amplifier unit for supplying such energization to the relay in response to said electromotive force; an amplifier unit including in combination an electron tube operable by current from the usual train 32 volt source of direct current, a filter and a bias means; said tube having a filament and a plate circuit independently connected to said direct current source to provide a predetermined normal plate circuit current in response to a given voltage of said source and a preselected grid bias voltage, said tube having a grid circuit connected to said receiver through a circuit means including said filter to efiect code variations of the plate circuit current in response to said electromotive force, said filter consisting of a first and a second condenser and a transformer having separate primary and secondary windings with the secondary winding constructed with multiple mid terminals, said filter disposed with said primary winding and first condenser connected in series to said receiver and said second condenser connected across the full portion of the secondary winding, and said filter tuned to resonance at the frequency of said alternating current to pass only said electromotive force and having a preselected portion of said secondary winding connected to said circuit means by a preselected one of said mid terminals to prmelect with the tuning undisturbed that portion of said electromotive force to be passed to said grid circuit as required to effect a predetermined code variation of said plate current, said bias means consisting of resistance connected across said direct ourrent source and having a mid terminal to which said grid circuit is connected to provide said preselected grid bias voltage and to vary such bias voltage directly with the voltage variations of said direct current source, and said plate circuit coupled to said relay to provide said energization or" the relay in response to said received electromotive force due to said construction of said filter and bias means.

3. In train control apparatus using a train carried code following relay to govern signaling means by supplying the relay with a given periodic energization in response to a coded electromotive force picked up by a train receiver from a coded alternating track circuit current, the combination comprising, an electron tube operable from the usual 32 volt direct current train source, a filter, said tube provided with a heater and a plate circuit connected in multiple to said train source and with a grid circuit coupled to said receiver through circuit means including said filter, a bias means consisting of a resistance connected across said train source and having a mid terminal to which said grid circuit is connected to provide said tube with a grid bias voltage that varies directly with the voltage of said-train source, said filter consisting of a first and a second condenser and a transformer having separate primary and secondary windings with the secondary Winding provided with a plurality of intermediate terminals, said filter disposed with the primary winding and the first condenser connected in series to said receiver and the full secondary winding and the second condenser connected in multiple to tune the filter to resonance at the frequency of said alternating current to suppress energy other than said electromotive force, and a preselected portion of said secondary winding coupled to said grid circuit by connection of said circuit means to a preselected one of said intermediate terminals to pass to the tube a preselected portion of said picked up electromotive force, and said plate circuit coupled to said relay whereby said relay is supplied with said given periodic energization for any one of a plurality of different effective values of alternating track circuit current and irrespective of variations in the voltage of said train current source.

l. In train control apparatus using a train carried code following relay tcgovern signaling means by supplying the relay with a. given periodic energization in response to a coded electromotive force picked up by a train receiver mm a coded alternating track circuit current, the combination comprising, an electron tube operable from the usual 32 volt direct current train source, a filter, said tube provided with a heater and a plate circuit independently connected to said train source and with a grid circuit coupled to said receiver through a circuit means including said filter, a fixed bias means consisting of a first and a second resistor connected in series across said train source and having a junction terminal connected to the cathode of said tube to include said second resistor in both said plate and grid circuits for supplying a grid bias voltage that effects a given normal plate circuit current irrespective of variations of plate and filament voltages due to voltage variations of said train source, said filter comprising capacitance and a transformer constructed with independent primary and secondary windings with the secondary winding equipped with multiple mid terminals to permit tuning of the filter at the frequency of said alternating current and selective connection of the circuit means to any one of said mid terminals for preselection with the tuning undisturbed of the value of the electromotive force to be applied to said grid circuit through said circuit means to predetermine the code variation of said plate circuit current for a given amplitude of track circuit current, an automatic bias means comprising a condenser and a resistor formed to have a time constant greater than the chi code eriod of said track circuit current and connected to said grid circuit to charge said condenser and provide an additional grid bias voltage when the amplitude of said track circuit exceeds said given amplitude for maintaining uniform code variation of the plate current, and said plate circuit coupled to said relay to supply said relay with said given periodic energization due to said code variation of the plate current.

5. In train control apparatus using a train carried code following relay to govern signaling means by supplying the relay with a given periodic energization in response to a coded electromotive force picked up by a train receiver from a coded alternating track circuit current, the combination comprising, an electron tube operable from the usual 32 volt direct current train source, a filter, said tube provided with a heater and a plate circuit independently connected to said train source and with a grid circuit coupled to said receiver through a circuit means including said filter, a fixed bias means consisting of a first and a second resistor connected in series across said train source and having a junction terminal connected to the cathode of said tube to include said second resistor in both said plate and grid circuits for supplying a grid bias voltage that effects a given normal plate circuit current irrespective of variations of plate and filament voltages due to voltage variations of said train source, filter comprising capacitance and inductance and tuned to resonance at the frequency of said alternating current to suppress energy picked up by said receiver other than said electromotive force, an automatic bias means comprising a condenser and a resistor formed to have a time constant greater than the oif code period of said track circuit current and connectcd to said grid circuit to charge said conde eer and provide an additional grid bias voltage when the amplitude of said picked up electromotive force exceeds the grid bias Voltage supplied by said fixed bias mean and thereby maintain uniform code variation of the plate circuit current, and said plate circuit coupled to said relay to supply said relay with said given periodic eneigization due to said code variation of the plate current.

In train control apparatus for use with a receiver mounted on a train to pick up an electrcrnotive force in response to a coded alternating track circuit current for control of signalingthe combination comprising, a train carried source of direct current, an electron tube having a filament and a plate circuit independently connected to said train source and a grid circuit coupled to said receiver, a first bias means including a first and a second resistor connected across said train source and having a junction ,eminal connected to said tube cathode to make said second resistor common to both the plate and grid circuits to supply a first grid bias voltage that varies directly with voltage variations of the train source to effect a given normal plate circuit current irrespective of changes in plate and filament voltages caused by voltage variations of the train current source, a filter including capacitance and a transformer having separate primary and secondary windings with the secondary winding provided with intermediate terminals, said filter tuned to resonance at the fr quency of said alternating current and interposed in said grid circuit coupling to pass from said receiver to said grid circuit only said electromotive force and to permit preselection at said intermediate terminal of the value of the electromotive force to be passed to effect a predetermined code variation of said plate circuit current for a given amplitude of the track circuit current, a second bias means including a condenser and a resistor formed with a time constant greater than the oil code period of said track circuit current and connected to said grid circuit to charge said condenser and supply an additional grid bias voltage to maintain aid predetermined code variation of the plate current when the track circuit current amplitude exceeds said given amplitude, a code following relay coupled to said plate circuit to periodically energize the relay in response to said code variations of the plate current, and circuit means controlled by relay to govern said signaling means.

7. In train control apparatus for use with a receiver mounted on a train to pick up an electromotive force in response to a coded alternating track circuit current for control of signaling means, the combination comprising, a train carried source of dire-ct current, an electron tube having a filament and a plat circuit independently connected to said train source and a grid circuit coupled to said receiver, a first bias means including a first and a second resistor connected across said train source and having a junction terminal connected to said tube cathode to make said second resistor common to both the plate and grid circuits to supply a first grid bias voltage that varies directly with voltage variations of the train source to effect a given normal plate circuit current irrespective of changes in plate and filament voltages caused by voltage variations of the train current source, a filter including capacitance and a transformer having separate primary and secondary windings with the secondary Winding provided with intermediate terminals, said filter tuned to resonance at the frequency of said alternating current and interposed in said grid circuit coupling to pass from said receiver to said grid circuit only said electromotive force and to permit preselection at said intermediate terminals of the value of the electromotive force to be passed to eiiect a predetermined code variation of said plate circuit current for a given amplitude of the track circuit current, a condenser interposed in series in said grid circuit, another resistor connected between said grid and the negative terminal of said train source, said condenser and said other resistor forming another bias means to supply an additional grid bias voltage to maintain said predetermined code variations of the plate current when the amplitude of the passed electromotive force exceeds said first grid bias voltage, said other resistor serving as a connection to retain said first grid bias voltage under open circuit conditions of said circuit, a code following relay coupled to said plate circuit to periodically energize the relay in response to said code variations of the plate current, and cirasecpec cuit means controlled by said relay to govern said signaling means.

8. In train control apparatus for use with a receiver mounted on a train to pick up an electromotive force in response to a coded alternating tra r; circuit current for control of signaling means, the combination comprising, a train carried source Of direct current, an electron tube having a filament and a plate circuit independently connected to said train source and a grid circuit coupled to said receiver, a first bias means including a first and a second resistor connected across said tr in source and having a junction terminal connected to said tube cathode to make said second resistor common to both the plate and grid circuits to supply a first grid bias voltage that varies directly with voltage variations of the train source to effect a given normal plate circuit current irrespective of changes in plate and filament voltages caused by voltage variations of the train current source, a filter including capacitance and a transformer having separate primary and secondary windings with the secondary winding provided with intermediat terminals, said filter tuned to resonance at the fre quency of said alternating current and interposed in said grid circuit coupling to pass from said receiver to said grid circuit only said electromotive force and to permit preselection at said intermediate terminals of the valu of the electromotive force to be passed to effect a predetermined code variation of said plate circuit current for a given amplitude of the track circuit current, a condenser interposed in series in said grid circuit, another resistor connected between said grid and the negative terminal or" said train source, said condenser and said other resistor forming another bias means to supply an additional grid bias voltage to maintain said predetermined code variations of tlie plate current when the amplitude of the passed electromotive force exceeds said first grid bias voltage, said other resistor serving as a connection to retain said first grid bias voltage under open circuit conditions of said grid circuit, a code following relay, a master transformer having one winding connected to said relay and another Winding interposed in said plate circuit in multiple with a by-pass condenser to periodically energize said relay in response to said code variations of the plate current and said other winding of the master transformer constructed with two separate lead wire at each end for independent connections to said lay-pass condenser and said plate circuit to avoid energization of the relay due to open circuit conditions of said plate circuit, and circuit means controlled by said relay to govern said signaling means.

9. In train control apparatus using a receiver mounted on a train to pick up an electromotive force in response to a coded alternating track circuit current and a code following rela operable to govern signalin means and coupled to said receiver through an amplifier unit to supply a predetermined energization of the relay in response to such electrornotive force, an amplifier unit including in combination, a low voltage electron tube having a filament and a plate circuit independently connected to the usual 32 volt direct current train source and a control grid circuit connected to said receiver through a filter, a first bias means including a first and a second resistor connected in series across said train source and having a junction terminal connected to the cathode of said tube to include said sec- 0nd resistor in both said plate and grid circuits to supply a first grid bias voltage that varies directly with the voltage or" said rain source to maintain a substantially uniform value of plate circuit current over a wide range of variations of the voltage of said train source, said filter including a first and a second condenser and a transformer having a secondar windin provided with mid terminals, said filter disposed with said first condenser and a primary winding of the transformer connected in series to said receiver and said second condense connected across the full portion of the secondary winding to tune the filter to resonance at the frequency of said alternating current, said grid circuit connected to a preselected one of said mid termi nals to preselect with said tuning unaffected the electromotive force to be applied to said tube required to cause a predetermined code variation of the plate circuit current for a given amplitude of track circuit current, a second bias means including a condenser and a resistor in multiple; said second bias means formed to have a time constant greater than the oil code period of said track circuit current and interposed in said grid circuit to supply an additional grid bias voltage to maintain said predetermined code variation the plate current when the amplitude of the track circuit current exceeds said given amplitude, and means to couple said plate circuit to said following relay to supply said predetermined energization of the relay in response to said predetermined code variation of the plate current.

10. In train control apparatus using a receiver mounted on a train to pick up an eleotromotive force in response to a coded alternating track circuit current and a code following relay operable to govern signaling means and coupled to said receiver through an amplifier unit to supply a predetermined energization of the relay in response to such electromotive force, an amplifier unit including in combination, a low voltage electron tube having a filament and a plate circuit independently connected to the usual 32 volt direct current train source and a control grid circuit connected to said receiver through a filter, a first bias means including a first and a second resistor connected in series across said train source and having a junction terminal connected to the cathode of said tube to include said sec ond resistor in both said plate andgrid circuits to supply a first grid bias voltage that varies directly with the voltage of said train source to maintain a substantially uniform value of plate circuit current over a wide range of variations of the voltage of said train source, said filter including capacitance and inductance and tuned to resonance at the frequency of said alternating current to pass only said picked up electromotive force and proportioned to apply a preselected value of said electromotive force as required to efiect a predetermined code variation of said plate circuit current in response to a given amplitude of said track circuit current, means including a transformer and a lay-pass condenser to couple said plate circuit to said relay to supply said predetermined energization of the relay in response to said code variation of the plate current, and another condenser connected across said grid and cathode of the tube to delay the leaking off of said grid bias voltage and avoid transfer of energy to said relay due to variation of the plate current because of an open circuit of said grid circuit.

11. In train control apparatus using a receiver mounted on a train to pick up an electromotive force in response to a coded alternating track circuit current and a code following relay operable to govern signaling means and coupled to said receiver through an amplifier unit to supply a predetermined energization of the relay in response to such electromotive force, an amplifier unit including in combination, a low Voltage electron tube having a filament and a plate circuit independently connected to the usual 32 volt direct current train source and a control grid circuit disposed to be supplied with said electromotive force through a filter, a first bias means including a first and a second resistor connected in series across said train source and having a junction terminal connected to the cathode of said tube to include said second resistor in both said plate and grid circuits to supply a first grid bias voltage that varies directly with the voltage of said train source to maintain a substantially uniform value of plate circuit current over a wide range of voltage variations of the train source, said filter tuned to resonance at the frequency of said alternating current to pass only said electromotive force and havin a plurality of mid output terminals to preselect the value of said electromotive force to be supplied to said grid circuit as required to effect a predetermined code variation of the plate current in response to a given amplitude of said track circuit current, a condenser interposed in series in said grid circuit, a third resistor connected between the control grid of the tube and the negative terminal of said train source, said condenser and third resistor forming a second bias means having a time constant greater than the off code period of the track circuit current to supply a second grid bias voltage when said supplied electromotive force exceeds said first grid bias voltage to maintain said predetermined code variation of the plate current when said track circuit current exceeds said given value, means including a transformer and a by-pass condenser to couple said plate circuit to said relay to supply said predetermined energization in response to said code variation of the plate current, and said third resistor to serve as a connection to maintain said first grid bias voltage to avoid such energization of the relay upon an open circuit condition of said grid circuit.

12. In train control apparatus using a receiver mounted on a train to pick up an electromotive force in response to a coded alternating track circuit current and a code following relay operable to govern signaling means and coupled to said receiver through an amplifier unit to supply a predetermined energization of the relay in response to such electromotive force, an amplifier unit including in combination, an indirectly heated electron tube having its filament and plate circuits connected to the usual 32 volt direct current train source, said filament circuit including a first resistor disposed adjacent the negative terminal of such source and said plate circuit including in series said first resistor and a second resistor disposed adjacent said tube cathode, a grid circuit for said tube connected to a control grid and said cathode to include said first and second resistors and disposed to receive said electromotive force through a filter, said first and second resistors forming a first bias means to supply a first grid bias voltage that varies substantially directly with the voltage of said train source to cause a substantially constant predetermined normal from said receiver value of plate circuit current irrespective of voltage variations of said train source, said filter tuned to resonance at the frequency of said alternating current to pass only said electromotive force and provided with multiple mid terminals to preselect the value of said electromotive force to be supplied to said grid circuit as required to effect a predetermined code variation of the plate circuit current in response to a given amplitude of said track circuit current, a condenser interposed in series in said grid circuit, a third resistor connected between said control grid and said negative terminal, said condenser and third resistor forming a second bias means having a time constant greater than the off code period of said track circuit current to supply a second grid bias voltage when said supplied electromotive force exceeds said first grid bias voltage to maintain said code variation of the plate current when the track circuit current exceeds said given amplitude, means including a transformer to couple said plat circuit to said relay to supply said predetermined energization in response to said code variation of the plate current, and said third resistor serving as a connection to maintain said first grid bias voltage to avoid energization of the relay due to an open circuit of said grid circuit.

13.111 train control apparatus using a receiver mounted on a train to pick up an electromotive force in response to a coded alternating track circuit current and a code following relay operable to govern signaling means and coupled to said receiver through an amplifier unit to supply a predetermined energization of the relay in response to such electromotive force, an amplifier unit including in combination, a first and a second indirectly heated electron tube each of which tubes has its filament and plate circuits connected to the usual 32 volt direct current train source, said first tube having its filament circuit including a first resistor disposed adjacent the negative terminal of said train source and its plate circuit including said first resistor in series with a second resistor adjacent said tube cathode, said first tube having a grid circuit connected to a control grid and said cathode to include said first and second resistors in series and disposed to receive said electromotive force, said first and second resistors forming a first bias means to supply to said first tube a grid base voltage that varies substantially directly with the voltage of said train source to cause a substantially constant predetermined normal value of plate circuit current for said first tube, means to couple the first tube plate circuit to a grid circuit for said second tube, a third and a fourth resistor connected in series across said train source and having a junction terminal connected to a cathode of the second tube to include said fourth resistor in both the second tube plate and grid circuits to supply to the second tube a grid bias voltage that varies directly with the voltage of said train source to cause a substantially constant predetermined normal value of plate circuit current for the second tube, and means including a transformer and a by-pass condenser to couple the second tube plate circuit to said relay whereby said relay is supplied with said predetermined energization in response to said track circuit current irrespective of voltage variations of said train source.

LESLIE R. ALLISON. CARL VOLZ. 

